When one room in a home in Novato, San Rafael, San Anselmo, Larkspur or Sausalito stays cold in winter and warm in summer, or a register barely moves air, the fault is often in the ductwork rather than the furnace or air conditioner. A run that came loose under the house, a section of flex duct crushed under storage, or decades-old tape that has let go can send a room’s air into the crawlspace instead. Duct repair finds those losses by testing and fixes them where they are.
How ducts fail in older Marin homes
- Disconnected runs. Ducts in crawlspaces get pulled apart by settling, by people moving around under the house and by animals. A fully disconnected run blows straight into the crawlspace.
- Crushed or kinked flex duct. In attics, flex duct gets stepped on, pinched behind framing or buried under stored boxes, and airflow drops to a trickle.
- Failed joints. Cloth duct tape dries out and lets go over the years, leaving every connection leaking a little.
- Sagging runs. Flex duct that is not supported often enough sags into a U shape, which slows air.
- Damaged insulation. Torn or missing duct wrap lets cool crawlspace air chill the warm air inside, or lets condensation form on cooling ducts in summer.
- Undersized returns. The house simply cannot get enough air back to the system, so the blower strains and some rooms starve.
Finding the problem: inspection and testing
We start with a duct system inspection from the furnace or air handler out to the registers, in the crawlspace or attic. Then we test:
- Pressure testing. The duct system is sealed at the registers and pressurized with a calibrated fan. The reading shows how much the ducts leak overall, before and after repair.
- Room-by-room airflow. We measure what each register delivers and compare it to what the room needs.
- Static pressure at the equipment, which tells us whether the ducts and returns are too restrictive for the blower.
- Visual tracing of every accessible run to find the actual leaks and damage.
You see the results and a repair plan with an itemized price before any work begins.
What the repair usually involves
| What we find | What it usually takes |
|---|---|
| Disconnected or loose runs | Reconnecting, fastening and strapping properly |
| Leaking joints and seams | Sealing with mastic or approved foil tape, not cloth tape |
| Crushed or torn flex duct | Replacing the damaged section |
| Sagging runs | Re-hanging with proper supports and straighter routing |
| Missing or wet insulation | Re-insulating the affected runs |
| Too little return air | Adding or enlarging a return path |
| Uneven rooms after sealing | Balancing with dampers so each room gets its share |
After the repair we test again so you can see the difference, and we check airflow at the rooms that started the call.
Duct repair or duct cleaning?
They solve different problems. Duct cleaning removes dust and debris from ducts that are intact. Repair fixes ducts that leak, sag or have come apart. If the ducts are leaking, repair comes first: a leaky return pulls in new dust from the crawlspace or attic as fast as it can be cleaned out. Some homes need both, in that order.
Hillside and older homes
On hillside lots in San Anselmo, Larkspur and Sausalito, long duct runs often snake through tight crawlspaces, and the rooms at the far end get the least air. In older houses, some duct wrap and tape may contain asbestos; if we see suspect material, we stop and recommend testing before anything is disturbed. Where a duct cannot be made to work well, a ductless mini-split for that room is sometimes the better answer.
For related symptoms see poor airflow, uneven temperatures and high energy bills. Town pages: duct repair in San Anselmo and in Larkspur.